Process for the production of ash-free adsorbent carbon



Patented May -5, 1931 3 UNITED srA'rEs PATENT OFFICE manor .1. mun, or near meme, mcnrean, ASSIGNOR 'ro moment sra'rn roam) or aearcunruan, or near nansme, MICHIGAN PROCESS FORFIHE PRODUCTION OF ASH-FREE AJJSORBENT CARBON Io Drawing.

One object of the resent invention is to produce adsorbent c arcoals derived from various sources which will be substantially free from ash and impurities, especially inorganic matter.

Another object is to produce activated charcoals from various sources in a degree of purit equal to that of the best grades of carbo ydrate charcoal.

A further object of the invention is to so.

standardize activated charcoals derived from- Adsorbent charcoals, because of their rela-.

tively reat activit have been used perhaps more requently t an other adsorbent material, both in the study and practice of adsorption of various materials from solution. It has been assumed that the material used was essentially pure carbon, and the role of other constituents was generally i nored. These adsorbents are, however, rea ly but poorly defined substances,'and the results obtained with them often showed considerable variation.

Many attempts have been made to purify these materials, but they have been unsuccessful as far as any appreciable reduction of the inorganic content was concerned. The usual procedure was to extract the charcoals with concentrated acids and occasionally fusion with alkali was attempted. A blood charcoal, understood to be purified b acids, has been a favored materlal for a sorption studies. But even this material has been found to contain approximately as hi h as eight percent of inorganic matter.

reudlich. and Losev found that the ash content of this material is not appreciably reduced by treatment with concentrated bydrochloric acid. They boiled the charcoal repeatedly with concentrated hydrochloric ac1d, then washed with hot distilled water, and finally with conductivity water. After Application filed November 11, 1927. Serial No. 282,709.

such treatment the ash-content was still from eight to five percent. Odn and An dersson used essentially the same method, but in addition subjectedthe charcoal to a final extraction with or anic solvents. Firth and Watson resorte to extraction with aqua regia. A blood charcoal which contained 8.82% of ash showed a reduction, after several days treatment, to 7.3%. Even after prolonged treatment for about a month the ash content was still 6.32%.

Only after very prolonged treatment could the ash content be appreciately reduced below this figure. But this drastic and prolonged treatment resulted in a considerable ---loss of the charcoal thus treated.

Commercial sugar charcoal contains normally much less ash, but treatment with concentrated hydrochloric acid in the usual -manner only reduced the ash content from 0.57 to 0.55 per cent. These illustrations are typical of the results hitherto obtained in t e efforts to purify adsorbent charcoals.

In In studies of adsorption of various materia I concluded that, in order to make the results of the investi ations of these adsorption phenomena uni orml reproducable and comparable, it was esirable to eliminate the complications and the differences resulting from the uncertain action of varying amounts of ash.

B my process of purification which will be escribed in further detail ereafter, I am able to produce activated charcoals from divers animal or vegetable sources in which the ash content can be reduced ordinarily to a few hundredths of one percent; and if the process be repeated a suflicient number of times, or if a charcoal with a low ash content 1s being treated, the reduction can be carried to less thanone hundredth of one per cent.

It has heretofore enerally been considered that charcoals 0% different origins have different and characteristic properties as to their ability to adsorb substances from solution. I have found, however, that such variations can be explained on the'basis of adsorbed substances on their surfaces or of mechanically held or occluded inorganic matter, and that the specific action ascribed to various charcoals wlth res ect to adsorption from solutions of acids, ases, and salts,

were really due to variations in the nature and extent of these impurities, as were also the contradictory data and conclusions concerning hydrolytic adsorption.

One of the outstanding characteristics of ure activated sugar charcoal is its capacity or adsorbing relatively large quantities of acids and its inability to adsorb even traces of strong inorgan c bases. I have found, however, that this is not a s ecific characteristic of su ar charcoal a one, and I have been able, y my process,-to so purify charcoals from various sources, as before indicated which will also adsorb acids very strongly, but will not adsorb the bases. Thus the adsorption results obtained with charcoals from any source will be comparable with those obtained from sugar charcoal, flprovided only that the ash content be su ciently reduced.

My rocess may be carried out in a number 0 ways, as will be obvious from the 'descri tion following, but my preferred proce ure is as follows: 1

Emam Ze.-A given charcoal after being thoroug 1y dried, is ground to a fineness to ermit it to pass through a 300-mesh sieve.

t is then mlxed in a latinum vessel with a suflicient quantity 0 a mixture of mineral acid, consisting of one part of hydrofluoric acid and five parts of h drochloric acid, to make a thin aste, wh1ch .is then warmed gently over a ow flame until most of the hydrofluoric acid has been driven off. After most of the acid has been thus expelled, the heating is increased to insure the complete removal of the acid. The charcoal is next boiled with concentrated hydrochloric acid, and is then diluted and filtered through hardened filter paper in a Biichner funnel. This extraction with concentrated h drochloric acid is repeated a second time, ai ter which the charcoal is washed .by repeated boiling with distilled water until most of the hydrochloric acid has been removed.

When the treatment of the charcoal has proceeded thus far the ash content has been reduced'to a few tenths of one percent, dew

ending upon the kind of charcoal used, the fineness to which it was reduced, etc.

In order to reduce the ash content still further, the charcoal is now dried in an oven, say at not less than about 115 0., and is then i nited at a tem erature of 900? to 1200 in silica vessels rom which the air is excluded to prevent oxidation and loss of carbon.

The above treatment with h drofluoric acid and extractions with hydroc loric acid are re ated until the desired purity has 65 been o tained. When the ash has been removed, the charcoal is ignited to drive ofi' the adsorbed acids, and is finally washed by boiling several times with a good grade of distilled water or conductivity water, and is then dried. The ignition drives off practically all the adsorbed acids. A minute quantity ofacid, however, still remains even after ignition, and, while this amount is negligible for most purposes, it may be removed readily b boiling a suspension of the charcoal in com uctivity water to which has been added approximately 1 cc. of a 0.02 N sodium or potassium hydroxide solution per gramme o charcoal. The excess alkali and morganic salt formed are then quantitatively removed by boiling and filtering three or four-times.

Thev process thus described in the foregoing example is susceptible to considerable modification without departing from the principle and scope-of the invention. Thus for instance, hydrofluoric acid alone may be used in the early step of the process instead of the mixture of hydrofluoric and hydrochloric acid. The function of the hydrofluoric acid is to attack the otherwise insoluble silicates and other ash constituents which are not readily decomposed by other mineral acids; no given concentration thereof need be employed for this purpose, but it may be used in varying strength as requirements may demand. I have on occasion found even greater dilutions than-that of 1: 5, as given in the example, to be effective.

What I claim as new and for which I pray the issuance of Letters Patent is:

1.- The process of purifying commercial grades of activated charcoal which consists of reducing the same to a fine powder, mixin with hydrofluoric acid, warming the mixture moderately until most of the acid is driven off, then increasing the temperature to effect the further removal of the acid, boiling with hydrochloric acid, diluting with distilled water and filtering, treating the recovered charcoal thus obtained repeatedly with hydrochloric acid, diluting with water, and filtering as before; drying and igniting the charcoal at a temperature ran ing between 900 to 1200 C. under exclusion of air.

2. The process of purifying commercial grades of activated charcoal comprising the steps of drying of the charcoal, reducing the same to fine powder of substantially 300 mesh, treating with a mixture of hydrofluoric acid and h drochloric acid in sufficient quantity to orm a thin paste, warming the mixture moderately until most of the acid is driven off, then increasing the temperature to effect the complete removal of the acid, boiling with concentrated hydrochloric acid, diluting with distilled water and filtering through, hardened filter paper;

subsequently treating the recovered charcoal again with concentrated h drochloric acid, diluting and filtering as be ore; then drying at a temperature of about C., and finally igniting the charcoal at a temperature ranging between 900 to 1200 C. under exclusion of air.

3. The process of purifying commercial grades of activated charcoal comprising admixture with hydrofluoric acid, removing the said acid, boiling with hydrochloric acid, and then removing the last named acid.

4. The process of purifying commercial grades of activated charcoal comprising admixture with a mixture of mineral acid containing hydrofluoric acid, removing the said acids, boiling with hydrochloric acid, and removing the last named acid.

,5. The process of purifying activated charcoal, comprising alternate treatments first with hydrofluoric acid and next with repeated treatments of hydrochloric acid, re peating this cycle of applications until all of the ash originally contained therein has been substantially removed.

6. The process of purifying activated charcoal, which consists of reducin the same to a powder, treating with a mixture of hydrofluoric acid and hydrochloric acid, warming the mixture until most of the acid is driven off, then increasing the tem erature to effect the complete removal 0 the acid, boiling with concentrated hydrochloric acid, diluting with distilled water and filtering, repeating the treatment with concentrated hydrochloric acid as before; then drying the charcoal and finally igniting it under exclusion of air; and then repeating the cycle of steps, above set forth, until substantially all of the impurities originally contained in the charcoal are removed.

ELROY J. MILLER. 

